Fluid control valves are known. These may be thought of as having either a single stage or as having multiple stages. In both forms, a valve spool is slidably mounted within a cylinder for controlled movement there along. When the valve spool is in a null position within the cylinder, various lands on the valve spool cover ports that communicate with the control outlets to prevent flow through the valve. The direction and magnitude of spool movement off-null controls the flows through the valve.
A single-stage or direct-drive valve generally has a motor or some other mechanism that directly engages the valve spool, and which selectively causes the spool to move off-null. A multiple-stage valve may have a pilot stage that controls movement of a valve spool in a second stage. The pilot stage may be a nozzle-flapper, jet-pipe or deflector-j et valve.